The avoidance of senescence is an essential property of tumor cells. We are planning to determine the role played by the WRN and potentially related RecQ helicases in the avoidance of oncogene-induced senescence. In particular, we will focus on the c-Myc oncogene as we have shown that c-Myc stimulates transcription of the WRN gene and more important, that the WRN protein is required to avoid cellular senescence induced by c-Myc overexpression. Loss of function mutations of WRN causes a human premature progeria, Werner Syndrome (WS), whose symptoms mimic aspects of natural aging. Cells derived from WS patients also show premature senescence, indicating that the organismal phenotype might be due to accelerated cellular senescence. We hypothesize that WRN function is required for the avoidance of senescence of tumor cells and thus may represent an attractive therapeutic target for cancer treatment. WRN protein participates in DNA repair of abnormal structures generated during DNA replication and aggravated by drugs that cause a DNA replication block. Indeed the preliminary data indicate that the senescence response of WRN deficient cells upon c-Myc overexpression is due to DNA damage and resultant cellular checkpoint responses. In this proposal we plan to test this hypothesis, thus defining the mechanisms of WRN and c-Myc co-dependence. These experiments will involve use of cells derived from WS patients (commercially available) as well as a variety of approaches to interfere with function/or expression of WRN in normal human fibroblasts and in human cancer cell lines. Finally, to assess the role of WRN in tumor development in vivo we will employ an established c-Myc induced lymphoma model in mice together with WRN knock-out mice. Ultimately, our goal is to provide a rational to develop WRN inhibitors to be employed in new therapeutic approaches for cancer. Our proposal is relevant to aging providing information on the basic function of WRN, a gene clearly implicated in organismal aging, and it is also of importance for cancer by defining how cells bypass senescence under oncogenic stimulation. This grant proposal focus on the hypothesis, supported by our previous work, that a gene involved in human aging, called the Werner Syndrome gene, is also involved in the "aging" process of tumor cells. In fact, it is known that cells in our body also age. Old cells eventually stop dividing, a condition referred to as irreversible cell-cycle arrest". This is incompatible with tumor cell growth and thus cancer cells have devised ways of avoiding aging. Our previous work demonstrated that the presence of WRN gene was necessary to avoid aging of normal cells when they carry an activated cancer gene. Now we would like to directly test if inhibition of WRN function in cell lines derived from human cancers will cause tumor cells to age or to stop growing. If so, drug inhibitors of WRN function could be proposed for the treatment of cancer.